Electrically tunable infrared reflector with adjustable bandwidth broadening up to 1100 nm

Abstract

A tunable infrared reflector has been fabricated using polymer stabilized cholesteric liquid crystals containing a negative dielectric, anisotropic liquid crystal and a long and flexible ethylene glycol twin crosslinker. The reflection bandwidth of this prototype smart window can be tuned from 120 nm to an unprecedented 1100 nm in the infrared region upon application of only a small DC electric field, without interfering with the incident visible solar light. Bandwidth broadening was induced using very low operational power with acceptable switching speeds but only takes place in cells with particular gap thicknesses. Calculations reveal that between 8% and 45% of incident solar infrared light can be reflected with a single cell. The infrared reflector can potentially be used as a smart window to maintain the indoor temperature throughout the year, thereby reducing reliance on artificial lighting, heating and cooling, resulting in more than 12% reduction of building operation costs.